Why am I unable to see AA sample when selected branch path tracing and unable to render animation when select GPU Compute on Mac?
I cannot help with your GPU because I don't have access to your computer. However, I was able to figure out the bluriness.

Problem

In your scene, one of the first things I noticed was that it was inside an enclosed space. Bluriness in enclosed spaces can often be caused by low lighting.

Solution

I selected the area lamp near the top of the cabin and turned up the Emission Strength to 1000 from 300. I also turned the Max Bounces: to 1024.

I also optimized the .blend file.

I made some adjustments in the Render tab of the Properties panel, namely that I set the Max: and Min: Light Path Bounces to 0 (for faster rendering). I also turned the Filter Glossy: value to 0.7. Additionally, I changed the resolution to just 1920x1080 (1080p; you had it set to 4k which really won't make any difference except causing the rendering to take 4 times as long). Furthermore, I turned the Sampling > Settings: > Clamp Indirect: value to 3.00. I turned the AA render samples to 100. Lastly, I optimized the Tile Size for CPU rendering (Properties panel > Render Tab > Performance Drop Down Menu > Tiles:). If you want it to be optimized for GPU rendering, change each (x/y) from 16 to 256.

On my 8-year-old mac with CPU and not all the image textures, one frame (probably) took a bit under an hour (I didn't wait for it to finish). On my Nvidia 970 4GB STRIX, one frame took just 54 seconds and looked like this:



Final Notes

Here is the fixed up .blend file:



I don't generally offer this (haven't before), but if you can get me a .blend file with all the images included, I will render it for you. 90 frames x 1 min each = about 90 min. --A fellow Blender-using student.